An analogue equivalent

Cabinet: Old-fashioned and, likely, you have never used one.

Illustration of a file cabinet (Powers et al. 2002)

Where to find files?

A filesystem is hierarchical contains 🌲

.
├── README.md
└── lectures
    ├── images
    │   └── ai.jpg
    ├── html
    │   ├── KED2024_01.html
    │   └── KED2024_02.html
    └── md
        ├── KED2024_01.md
        └── KED2024_02.md

How to describe the location of a file?

• absolute paths start from top-level directory
  • begins with / (uppermost folder)
  • e.g. /home/alex/KED2024/slides/KED2024_01.html
• relative paths when looking from current directory
  • begins with the name of a folder or file
  • e.g. KED2024/slides/KED2024_01.html

What is the path?

You are in /home/myuser/documents containing
the subfolders pictures and texts.

• What is the absolute path to texts?

• What is the relative path to texts?

Important places in your file system

• shortcut names of directories

  • . current dir
  • .. parent dir
  • ~ home dir (e.g. /home/alex)

• find your files on Windows

  • /mnt/c/Users/USERNAME/ (replace with your USERNAME)
  • shortcut via documents

Navigating in a file system

pwd                 # show absolute path of current directory

ls                  # list content of current directory
ls -lh              # list with more information
ls dirname          # list content of directory dirname

cd ..               # change directory to go folder up
cd dir/subdir       # go to folder dir/subdir (two folders down)

open .          # open path in Finder (macOS)
explorer.exe .  # open Explorer in WSL Ubuntu (Windows)

Open text files

Show within Shell

more text.txt           # print content (spacebar to scroll)

head text.txt           # print first 10 lines of file
tail -n 5 text.txt      # print last 5 lines of file

Useful key actions

• autocompletion: TAB
• history of used commands: ⬆️
• scrolling: SPACEBAR
• cancel: CTRL + C
• quit: q or CTRL + D

Create files and directories

touch test.txt          # create a new file

mkdir data              # make a new directory
mkdir -p data/1999      # make a new directory with a subfolder

Copy and move files

cp test.txt other_folder/      # copy file into other folder
mv test.txt new_name.txt       # rename a file
mv test.txt other_folder/      # move file into other folder

Remove files

Watch out, there is no recycle bin. No way back!

rm old.txt          # remove a file
rm -r old_data      # remove a folder with all its files

In-class: Exercises I

1. Create a new directory called tmp in your home directory.
2. Change into that directory using cd and print its absolute path using pwd.
3. Use touch to create a new file called magic.txt in tmp.
4. Rename the file from magic.txt to easy_as_pie.txt.
5. Find the easy_as_pie.txt file using your graphical file manager (Windows: Explorer, Mac: Finder)
6. Check out the helper page of mv command.
7. Look around in the filesystem using cd and ls. Where are your personal files located?

Follow conventions 🙏

• no spaces/umlauts in names
  • only: alphanumeric, underscore, hyphen, dot
• files have a suffix, folders don’t
  • text_1.txt vs. texts
• descriptive file names
  • SOURCE/YEAR/speech_party_X.txt

Wildcards

Placeholders to match …

• any single character: ?
• any sequence of characters: *

mv data/*.txt new_data/.    # move txt-files from to another subfolder
cp *.txt files/.            # copy all txt-files in a single folder

Searching

List certain files only

# list all files with the suffix .txt (in current directory)
ls *.txt

Find term across files

# find all files containing X in provided directory 
grep -r "Europe" /path/to/dir   

Operators

Combining commands

Use shell operators to …

• redirect output into file (overwrite): >
• append to existing file: >>
• stream to next command: | (pipe)

echo 'line 1' > test.txt    # write into file
more test.txt | tail -n 1   # pass output to next command

Learn more about operators ⚙️

Merging files

cat part_1.txt part_2.txt       # concatenate multiple files
cat *.txt > all_text.txt        # merge all txt into a single one

In-class: Exercises II

1. Create a new file with touch.

2. Write the following content into that file, one line at a time using the append operator:

   How about making programming a little more accessible? Like:
   from human_knowledge import solution

3. Make sure that the content was written into that file using more.

In-class: Exercises III

1. Navigate up and down in in your filesystem using cd and list the respective files per directory with ls. Where can you find your personal documents? Print the absolute path with pwd.
   Windows users may have a look at /mnt/c/Users since they are working on a Ubuntu subsystem.

2. Read man ls and write an ls command that lists your documents ordered

   • by recency (time)
   • by size

3. Use the | and > operators to write the 3 “last modified” files in your documents folder into a file called last-modified.txt on your desktop (desktop is also a directory). Write a single command performing multiple operations using operators.

Additional resources

Useful intros to Bash

• Cheatsheet for this course
• Introduction to the Bash Command Line by The Programming Historian
• An Introduction to the Linux Terminal by DigitalOcean
• The Unix Shell by Software Carpentry